Mold for producing single crystals

ABSTRACT

The mold is intended for producing single cast articles and is adapted for multiple casting having a central mold portion with lateral branches from the sides of which single crystals grow into the article molds.

United States Patent Barry J. Piearcey Galmpton, Brixham, Devon, England 746,577

July 22, 1968 Mar. 9, 1971 United Aircraft Corporation East Hartford, Conn.

Inventor Appl. No. Filed Patented Assignee MOLD FOR PRODUCING SINGLE CRYSTALS 14 Claims, 4 Drawing Figs.

U.S. Cl 164/353, 164/60, 164/127, 164/361 Int. Cl B22d 15/0 B22d 25/06 Field of Search 164/60, 127, 338, 353, 361; 148/1.6;23/(Inquired); 415/177, 216; 416/241 [56] References Cited UNITED STATES PATENTS 3,204,303 9/1965 Chandley 164/127X 3,342,455 9/1967 Fleck et al. 253/77 3,376,915 4/1968 Chandley l64/60UX 3,441,078 4/1969 Chandley 164/361X Primary ExaminerJ. Spencer Overholser Assistant Examiner-John E. Roethel Attorney-Charles A. Warren ABSTRACT: The mold is intended for producing single crystal cast articles and is adapted for multiple casting having a central mold portion with lateral branches from the sides of which single cyrstals grow into the article molds.

MOLD FOR PRODUCING SINGLE QRYSTALS BACKGROUND OF THE INVENTION SUMMARY OF INVENTION A feature of this invention is a'mold that is adapted to produce single-crystal cast articles free of inclusions and with the desired dendritic orientation with respect to the axis of the cast article.

Another feature is an arrangement by which to produce a plurality of cast articles at one time in a single mold, all with the appropriate crystalline orientation.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a horizontal sectional view of a mold construction along broken line 1-1 of FIG..2.

FIG. 2 is a vertical sectional view of the mold substantially along the line 2-2 6f FIG. I with one of the side branches broken away.

FIG. 3 is a vertical sectional view of the mold of FIG. 1 at right angles to FIG. 2 and the broken lines 3-3 of FIG. 1.

F10. 4 is a sectional view of a modification of the article portion of the mold.

DESCRIPTION OF THE PREFERRED EMBODIMENT The mold of the invention is a shell mold and may be produced by making a wax pattern of the entire cast structure, then successively dipping the pattern in mold material until an adequate thickness of shell is built up. The mold is then cured at a temperature that will melt the wax so it flows out of the mold. This is now a well established technique and not a part of the present invention. The latter involves the mold arrangement to produce the desired results. The single-crystal cast article is described and claimed in the above-identified Piearcey U.S. Pat. No. 3,494,809. The mold of the invention is hollow throughout and has a central starter portion -2 preferably square in cross section with an open lower end 4 that is adapted to rest on a chill plate 6 during the casting process. The chill plate causes controlled solidification by heat removal from the metal or alloy at a selected rate. The starter portion 2 has a constriction 8 therein at a point spaced from the open lower end such that above this constriction the starter portion is smaller in cross-sectional area but of substantially constant cross-sectional area for the remainder of the starter portion to the top thereof. In this way only the central portion of the grain growth directly above the chill plate is continued into the smaller dimension of the starter portion.

Grain growth in columnar form, as described in the Ver- Snyder U.S. Pat. No. 3,260,505 is started at the chill plate and is propagated upward as solidification occurs. The mold is held at a temperature above the melting point of the alloy until the alloy is poured so that solidification will begin only at the chill plate. It will be understood that the columnar grains in the starter portion have a preferred (001) orientation. They are represented in FIG. 1 by the column ends 10.

Mounted on opposite sides of the starter portion 2 and at a point below the top thereof and above the restriction 8 are lateral branch portions 12 also preferably rectilinear in cross section. Each branch portion I2 has an upward slope away from the starter portion, as shown. Directly below the attachment of each branch portion to the starter portion there is a small constriction 14 extending across the side of the starter portion to which the branch portion is attached. This constriction materially reduces the number of columnar grains at this point and promotes a coarsening of the grains. Only these grains exposed to the branch portion above this constriction grow laterally into the branch and these grains then become platelike as represented by the individual grains 16 FIG. 1. Thus only a few columnar grains are formed in these branch portions and most of the grains extend substantially the length ofthe branch portion.

The article mold portions 18 are attached to the sides of the branch portions at points spaced from the ends of the branches by transverse connecting mold portions 20 which have a slope upward from the branch portion. Just before the attachment of the transverse mold portions the branch portion has a constriction 22 along each side of the branch portion to which the transverse portion is attached. This reduces the grain growth in this areaand assures the location of a single platelike grain at the inlet end of each transverse portion. Thus, in these transverse portions, there will be only a single grain growth and this will continue into the article mold.

The article mold shown is a turbine blade mold having a root section 24 at the base where it attaches to the transvers portion, an airfoil section 26 and a shroud section 28. The longitudinal axis of this mold passes through the root, airfoil and shroud sections and is the axis along which the blade has the highest loading in operation. It is along this axis that the (00l orientation should be and thus the longitudinal axis is located at right angles to the bottom opening in the mold and thus at right angles to the chill plate. Thus the vertical orientation of the dendritic growth in the columnar grains in the starter portion is continued into the dendritic growth in article portions all in parallel relation.

The transverse portions are also preferably rectangular in cross section and, adjacent to the outer end, each transverse portion has a freckle catcher or blind riser 30 consisting of an upwardly extending recess in the mold. This recess receives any foreign particles floating on the liquid metal or alloy so that they are excluded from the article portion of the mold. These foreign particles if not entrapped may serve as nucleation sites for undesired grain growth. The appearance of these grains on the surface of the cast article is referred to as freckling.

The extension of the starter portion 31 beyond the branch attachment, and the extension of the branch portions 33 beyond the transverse attachments provides improved perfection of grain orientation and serves as added pockets for entrapment of inclusions. The several features above described each contributes in its way in assuring a single-crystal cast article free of inclusions and surface defects and with the desired crystalline orientation.

It will be understood that the mold also includes a pouring sprue by which the mold may be filled with metal or alloy. In the arrangement shown this sprue 32 is attached to the top ends of the several article portions to assure complete filling of the entire mold including each article portion. It will be understood that the orientation of the dendritic structure of the single crystal in each article may be controlled by appropriate orientation of the axis of the article portion with respect to the chill plate.

As shown in FIG. 4, it may be desirable to add additional freckle catchers in the article portion of the mold. To this end there are provided recesses 34 at the leading and trailing edges of the airfoil section 26 of the article portion of the mold in which any impurities remaining on the surface of the liquid metal or alloy will be collected. These recesses form projections 36 on the cast article which are removed by appropriate machining to produce the desired contour at leading and trailing ends of the airfoil section of the finished article.

Iclaim:

1. A mold for producing directionally-oriented, singlecrystal castings, the mold being positioned on a chill plate for the casting operation, said mold including a central starter portion open at its lower end to rest on the chill plate at least one lateral branch extending laterally from and connected at the side of the central portion at a point spaced from the open lower end thereof, said branch having a substantially vertical side opening therein substantially parallel to the longitudinal axis of the lateral branch, and at least one substantially vertically arranged article mold attached laterally at the lower end thereof to the side of the lateral branch at said side opening and extending upwardly therefrom, said article mold being in substantial horizontal communication with the lateral branch through said side opening in said branch, the longitudinal axis of the article mold extending substantially at right angles to the open end of the starter portion.

2. A mold as in claim 1 in which the article mold portion is connected to the lateral branch by a transverse connecting mold portion.

3 A mold as in claim 1 in which the article mold portion is attached to the lateral branch at a point spaced from the outer end thereof.

4. A mold as in claim 1 in which there are at least two lateral branches and at least two article mold portions in opposed relation on each lateral branch.

5. A mold as in claim 1 in which there is protuberance on the lateral branch close to the article mold portion and at a point between the article mold portion and the central starter portion to form a constriction.

6. A mold as in claim 1 in which a freckle catcher is formed at point of attachment of the article mold portion to the lateral branch in the form of an upwardly extending recess in the mold.

7. A mold as in claim 1 in which the lateral branch extends from the central portion at a point below the top thereof.

8. A mold for producing directionally-oriented, singlecrystal castings, the mold being positioned on a chill plate for the casting operation, said mold including a central starter portion having its lower end open to rest on the chill plate, said portion extending substantially vertically, at least one lateral branch portion extending outwardly from the side of the central portion at a point below the top thereof, and at least one article mold attached at the side of the lateral branch portion at a point spaced from the end of the branch portion.

9. A mold as in claim 8 in which there is a restriction in the central starter portion below the lateral branch.

10. A mold as in claim 8 in which there is a restriction in the lateral branch between the starter portion and the attachment point of the article mold.

11. A mold as in claim 8 in which there is a transverse connecting mold portion between the lateral branch and the article mold.

12. A mold as in claim 11 in which there is a blind riser in the transverse connecting mold portion adjacent to the article mold.

13. A mold as in claim 8 in which there are a plurality of lateral branch portions projecting from the starter portion, and a plurality of article molds on the sides of each lateral branch and in which the longitudinal axes of the article molds are oriented with respect to the open lower end of the starter portion to produce the desired orientation in the cast article.

14. A mold as in claim 8 in which the central starter portion is reduced in cross-sectional area at a point between the open bottom end and the attachment of the lateral branch thereto. 

2. A mold as in claim 1 in which the article mold portion is connected to the lateral branch by a transverse connecting mold portion.
 3. A mold as in claim 1 in which the article mold portion is attached to the lateral branch at a point spaced from the outer end thereof.
 4. A mold as in claim 1 in which there are at least two lateral branches and at least two article mold portions in opposed relation on each lateral branch.
 5. A mold as in claim 1 in which there is protuberance on the lateral branch close to the article mold portion and at a point between the article mold portion and the central starter portion to form a constriction.
 6. A mold as in claim 1 in which a freckle catcher is formed at point of attachment of the article mold portion to the lateral branch in the form of an upwardly extending recess in the mold.
 7. A mold as in claim 1 in which the lateral branch extends from the central portion at a point below the top thereof.
 8. A mold for producing directionally-oriented, single-crystal castings, the mold being positioned on a chill plate for the casting operation, said mold including a central starter portion having its lower end open to rest on the chill plate, said portion extending substantially vertically, at least one lateral branch portion extending outwardly from the side of the central portion at a point below the top thereof, and at least one article mold attached at the side of the lateral branch portion at a point spaced from the end of the branch portion.
 9. A mold as in claim 8 in which there is a restriction in the central starter portion below the lateral branch.
 10. A mold as in claim 8 in which there is a restriction in the lateral branch between the starter portion and the attachment point of the article mold.
 11. A mold as in claim 8 in which there is a transverse connecting mold portion between the lateral branch and the article mold.
 12. A mold as in claim 11 in which there is a blind riser in the transverse connecting mold portion adjacent to the article mold.
 13. A mold as in claim 8 in which there are a plurality of lateral branch portions projecting from the starter portion, and a plurality of article molds on the sides of each lateral branch and in which the longitudinal axes of the article molds are oriented with respect to the opeN lower end of the starter portion to produce the desired orientation in the cast article.
 14. A mold as in claim 8 in which the central starter portion is reduced in cross-sectional area at a point between the open bottom end and the attachment of the lateral branch thereto. 